Protective coating and process for producing the same

Abstract

A coating ( 4 ) that is metallurgically bonded to a metal substrate ( 2 ) to protect the substrate includes carbide precipitates ( 10 ) of irregular and angular shape and a matrix ( 12 ) in which the precipitates are embedded. In a flame spraying procedure that utilizes a wire having a metal case and a core containing metal carbides, metals are deposited on the substrate as a basic coating. When that coating is subjected to a carbon rich environment, the carbon unites with the more reactive metals in the basic coating to form carbide precipitates of those metals, leaving the remaining metals to form the matrix. The carbide precipitates possess irregular and angular configurations and remain firmly embedded in the matrix, even though some of the matrix may disappear through the effects of erosion, corrosion, abrasion or wear.

1 . (canceled) 
   
   
       2 . (canceled) 
   
   
       3 . (canceled) 
   
   
       4 . (canceled) 
   
   
       5 . (canceled) 
   
   
       6 . (canceled) 
   
   
       7 . (canceled) 
   
   
       8 . (canceled) 
   
   
       9 . (canceled) 
   
   
       10 . (canceled) 
   
   
       11 . (canceled) 
   
   
       12 . (canceled) 
   
   
       13 . (canceled) 
   
   
       14 . (canceled) 
   
   
       15 . (canceled) 
   
   
       16 . A structure comprising:
 a substrate comprising metal, and   a basic coating mechanically bonded to the substrate, the basic coating comprising a first metal and a second metal, and having essentially no carbides and a porosity of about 5% to about 15%;   wherein the first metal will form a carbide in preference to the second metal if the basic coating is exposed to a reducing environment containing carbon at an elevated temperature.   
   
   
       17 . The structure according to  claim 16 , wherein the elevated temperature is within the range of about 1200° F. to about 1800° F. 
   
   
       18 . The structure according to  claim 16 , wherein the first metal comprises a material selected from the group consisting of:
 tungsten;   titanium;   chromium; and   tantalum.   
   
   
       19 . The structure according to  claim 16 , wherein the second metal comprises nickel. 
   
   
       20 . The structure according to  claim 16 , wherein the second metal comprises cobalt. 
   
   
       21 . The structure according to  claim 16 , wherein after an exposure to said reducing environment containing carbon at an elevated temperature the basic coating forms a protective coating comprising a metal matrix, the matrix comprising carbide precipitates formed predominantly of the first metal, the carbide precipitates being embedded in and interlocking with the matrix and having an irregular shape. 
   
   
       22 . The structure according to  claim 21 , wherein the carbide precipitates comprise a dendridic structure. 
   
   
       23 . The structure according to  claim 21 , wherein the exposure of the basic coating to said reducing environment containing carbon at an elevated temperature occurs during use of the structure of which the substrate is a part. 
   
   
       24 . A process for providing a metal substrate with a protective coating, said process comprising:
 depositing a plurality of metals on the substrate through the application of heat to form a basic coating that is essentially metals bonded to the substrate, the basic coating comprising a first metal and a second metal, and having a porosity of about 5% to about 15%, wherein the first metal will form a carbide in preference to the second metal if the basic coating is exposed to a reducing environment containing carbon at an elevated temperature;   heating the basic coating bonded to the substrate to the elevated temperature; and   exposing the basic coating bonded to the substrate to a reducing environment having carbon while at the elevated temperature, so that the carbon combines predominantly with the first metal in the basic coating to form the protective coating having precipitated carbides embedded in a metal matrix within said protective coating.   
   
   
       25 . The process according to  claim 24 , wherein the basic coating is deposited by thermal spraying. 
   
   
       26 . The process according to  claim 25 , wherein the basic coating is derived from a wire comprising a metal case and a core containing metal carbides. 
   
   
       27 . The process according to  claim 26 , wherein depositing a plurality of metals comprises heating the wire hot enough to melt the case and to disassociate the carbon from the metal of the carbides of the core. 
   
   
       28 . The process according to  claim 27 , wherein the carbon liberated from the metals of the carbide combines with oxygen to form carbon dioxide. 
   
   
       29 . The process according to  claim 28 , wherein the formation of carbon dioxide reduces the level of oxidation of one or more of said plurality of metals during the step of depositing a plurality of metals on the substrate through the application of heat to form a basic coating. 
   
   
       30 . The process according to  claim 24 , wherein one or both of the steps of heating the basic coating bonded to the substrate to the elevated temperature, and exposing the basic coating bonded to the substrate to a reducing environment having carbon while at the elevated temperature, occurs during use of the substrate following the step of depositing a plurality of metals on the substrate through the application of heat to form a basic coating. 
   
   
       31 . The process according to  claim 30 , wherein said use comprises one or more steps of a coal gasification process. 
   
   
       32 . The process according to  claim 24 , wherein the elevated temperature is within the range of about 1200° F. to about 1800° F. 
   
   
       33 . The process according to  claim 24 , wherein the protective coating is metalurgically bonded to the substrate.